1. Field of the Invention
The present invention generally relates to an electronic device, a standoff member, and an electronic-device manufacturing method. More particularly, the present invention relates to an electronic device having the structure in which a semiconductor device and a mounting substrate are bonded together by flip-chip bonding with a predetermined standoff therebetween, and a method of manufacturing the electronic device.
2. Description of the Related Art
FIG. 1 shows the outline composition of a conventional electronic device 1. The conventional electronic device 1 of FIG. 1 generally contains the semiconductor device 2, the system board 3, and the heat sink 4.
The semiconductor device 2 has a BGA (ball grid array) type package structure and comprises the semiconductor chip 5, the package substrate 6, the lid 7, and the bumps 8. The flip-chip bonding of the semiconductor chip 5 is performed on the top surface of the package substrate 6.
Moreover, the plurality of bumps 8 are arranged on the bottom surface of the package substrate 6. The package substrate 6 is the multi-layer substrate and functions as an interposer which electrically connects the bumps 8 on the bottom surface of the package substrate 6 to the semiconductor chip 5 on the top surface of the package substrate 6.
Moreover, the lid 7 is arranged on the top surface of the package substrate 6 on which the semiconductor chip 5 is carried in order to protect the semiconductor chip 5 from dusts or damage.
Furthermore, the bumps 8 (solder balls) are arranged on the bottom surface of the package substrate 6, and the package substrate 6 is soldered to the system board 3 via the bumps 8. Thereby, the flip-chip bonding of the semiconductor device 2 to the system board 3 is formed.
On the other hand, the heat sink 4 is formed in order to dissipate the heat generated by the semiconductor chip 5 into the atmosphere. The semiconductor device 2 mentioned above is arranged on the top of the base 13, and the heat sink 4 is arranged on the top of the lid 7 through the heat transfer material 9.
The heat sink 4 is pressed onto the base 13 by the springs 10, so that the heat sink 4 contacts the lid 7 firmly under pressure. Therefore, thermal conduction of the heat generated by the semiconductor chip 5 to the heat sink 4 readily occurs through the lid 7 and the heat transfer material 9, and the heat sink 4 dissipates the heat into the atmosphere effectively.
In recent years, the quantity of the heat generated by the semiconductor chip 5 is increasing on a yearly basis with the improvement in the performance of the electronic system on which the electronic device 1 is carried. In order to improve the cooling performance, the size expansion of the heat sink 4, the material change of the heat sink 4 (for example, aluminum is changed to copper), etc. have been achieved. In connection with this, the weight of the heat sink 4 is increasing and the loading force of the springs 10 to press the heat sink 4 onto the semiconductor device 2 firmly is also increasing.
Thus, the difficulty arises in that the bumps 8 (solder balls) receive the increased weight of the heat sink 4, and the increased loading force of the springs 10, and fracture of the bumps 8 may occur if all the weight and the loads are impressed on the bumps 8.
Even though the fracture does not occur, deformation of the bumps 8 may occur, and the clearance between the system board 3 and the package substrate 6 becomes too narrow and uneven. In such circumstances, the deformation of the bumps 8 will cause a short circuit between the adjoining bumps 8.
Hereinafter, the clearance between the system board (mounting substrate) and the package substrate will be referred to as the standoff.
To obviate the above problem, arranging a standoff member (spacer) between the system board 3 and the package substrate 6 is known.
FIG. 2 shows the bonded portion between the system board 3 and the package substrate 6 in the conventional electronic device 1 of FIG. 1 in the vicinity of the standoff member.
In the conventional example of FIG. 2, the standoff member 11 is soldered to the package substrate 6 through the solder 12. The predetermined standoff is formed between the system board 3 and the package substrate 6 by this standoff member 11.
The weight of the heat sink 4 and the loading force of the springs 10 can be received by the standoff member 11 mainly, and the use of the standoff member 11 enables the force impressed to the bumps 8 to be reduced. For this reason, it is possible to prevent the deformation or fracture of the bumps 8, and, therefore, the package substrate 6 and the system board 3 can be electrically connected safely.
Moreover, the standoff member is not restricted to the composition shown in FIG. 1 and FIG. 2, and standoff members in various kinds of composition have been proposed.
Specifically, Japanese Laid-Open Patent Application No. 10-013012 discloses an example of the standoff member which employs a resin spacer provided between a semiconductor device and a system board (mounting substrate). Moreover, Japanese Laid-Open Patent Application No. 09-213743 discloses a spacer portion (standoff member) which defines a predetermined standoff between a semiconductor device and a wiring substrate, and this spacer portion is inserted in the positioning hole of the semiconductor device and the positioning hole of the wiring substrate in common. The spacer portion is arranged approximately in the center of the positioning pins which are provided for positioning of the semiconductor device and the wiring substrate.
In the conventional technology of FIG. 1 and FIG. 2, the standoff member 11 is fixedly soldered to the package substrate 6 by the solder 12. For this reason, it is necessary to improve the soldering wettability of the soldering surface of the standoff member 1. The surface treatment, such as Au plating, is required for the surface of the standoff member 11 confronting the solder 12 for this purpose, which causes the manufacturing cost to increase.
Moreover, the material and configuration of the standoff member 11 are different from those of the bumps 8, and there is the problem in that special consideration must be taken to the positioning and handling of the standoff member 11 and the bumps 8, which causes the efficiency of manufacture of the electronic device 1 to fall.
On the other hand, in the method of Japanese Laid-Open Patent Application No. 10-013012, the resin spacer is used as the standoff member. For this reason, additional equipment for filling the resin in the space between the semiconductor device and the mounting board is required, which causes the equipment and facility cost to increase.
Moreover, in order to cure the resin, additional heat-treatment is required. Since the height of the resin spacer on the mounting board just after the filling of the resin is completed is still uneven, the leveling procedure is also needed. Therefore, the use of the resin spacer will make the manufacturing processes complicated.
Furthermore, in the method of Japanese Laid-Open Patent Application No. 09-213743, the positioning of the semiconductor device and the wiring substrate is performed with the positioning pins in which the spacer portion (standoff member) is provided. For this reason, it is necessary to carry out the machining of the positioning pins and the positioning holes with high precision. The preparation of such positioning pins and holes is difficult and troublesome, and the manufacturing cost will be raised.